In-Silico Determination of Insecticidal Potential of Vip3Aa-Cry1Ac Fusion Protein Against Lepidopteran Targets Using Molecular Docking

Overexpression of the AGL42 gene in cotton delayed leaf senescence through downregulation of NAC transcription factors

Premature leaf senescence negatively influences the physiology and yield of cotton plants. The conserved IDLNL sequence in the C-terminal region of AGL42 MADS-box determines its repressor potential for the down regulation of senescence-related genes. To determine the delay in premature leaf senescence, Arabidopsis AGL42 gene was overexpressed in cotton plants. The absolute quantification of transgenic cotton plants revealed higher mRNA expression of AGL42 compared to that of the non-transgenic control. The spatial expression of GUS fused with AGL42 and the mRNA level was highest in the petals, abscission zone (flower and bud), 8 days post anthesis (DPA) fiber, fresh mature leaves, and senescenced leaves. The mRNA levels of different NAC senescence-promoting genes were significantly downregulated in AGL42 transgenic cotton lines than those in the non-transgenic control. The photosynthetic rate and chlorophyll content were higher in AGL42 transgenic cotton lines than those in the non-transgenic control. Fluorescence in situ hybridization of the AG3 transgenic cotton line revealed a fluorescent signal on chromosome 1 in the hemizygous form. Moreover, the average number of bolls in the transgenic cotton lines was significantly higher than that in the non-transgenic control because of the higher retention of floral buds and squares, which has the potential to improve cotton fiber yield.

Function of CTLGA9 Amino Acid Residue Leucine-6 in Modulating Cry Toxicity

Aedes aegypti is a crucial vector for many arboviral diseases that cause millions of deaths worldwide and thus is of major public health concern. Crystal (Cry) proteins, which are toxins produced by Bacillus thuringiensis, are structurally organized into three-domains, of which domain II is the most variable in terms of binding towards various toxin receptors. The binding of Cry11Aa to putative receptor such as aminopeptidase-N (APN) is explicitly inhibited by midgut C-type lectins (CTLs). The similarity between the domain II fold of Cry11Aa toxin and the carbohydrate recognition domain in the CTLs is a possible structural basis for the involvement of Cry domain II in the recognition of carbohydrates on toxin receptors. In this study, a site-directed point mutation was introduced into the A. aegypti CTLGA9 gene on the basis of molecular docking findings, leading to substitution of the Leucine-6 (Leu-6) residue in the protein with alanine. Subsequently, functional monitoring of the mutated protein was carried out. Unlike the amino acid residues of wild-type CTLGA9, none of the residues of mutant (m) CTLGA9 were competed with Cry11Aa for binding to the APN receptor interface. Additionally, ligand blot analysis showed that both wild-type and mutant CTLGA9 had similar abilities to bind to APN and Cry11Aa. Furthermore, in the competitive ELISA in which labeled mutant CTLGA9 (10 nM) was mixed with increasing concentrations of unlabeled Cry11Aa (0–500 nM), the mutant showed no competition with Cry11Aa for binding to APN., By contrast, in the positive control sample of labeled wild type CTLGA9 mixed with same concentrations of Cry11Aa competition between the two ligands for binding to the APN was evident. These results suggest that Leucine-6 may be the key site involved in the competitive receptor binding between CTLGA9 and Cry11Aa. Moreover, according to the bioassay results, mutant CTLGA9 could in fact enhance the toxicity of Cry11Aa. Our novel findings provide further insights into the mechanism of Cry toxicity as well as a theoretical basis for enhancing the mosquitocidal activity of these toxin through molecular modification strategies.

K. S, Thakur S, Rathore M, Verma OP, Singh NP, Das A. Evaluation of transgenic chickpea harboring codon-modified Vip3Aa against gram pod borer (Helicoverpa armigera H.)

The gram pod borer is a major pest of chickpea, accounting for average annual yield losses to the tune of 40-50%. VIP3Aa, a class of insecticidal protein with different receptor binding site in the insect's midgut compared to Bt-crystal protein, offers an alternative protection strategy against Lepidopteran insects. Here, we report evaluation of genetically engineered chickpea lines harboring codon modified Vip3Aa (cmVip3Aa) against the Lepidopteran insect pest, gram pod borer. The synthetic codon modified, cmVip3Aa gene of 2,370 bp was sub-cloned in modified plant expression vector and used for direct transformation of embryonic axis explants of chickpea (cv. DCP 92-3), with transformation efficiency of 4.30%. Presence and transmission of transgene across two generations were confirmed by PCR and Southern blot analyses in the five selected transgenic chickpea lines. Real Time PCR analyses indicated variable levels of cmVip3Aa expression in the transgenic chickpea lines (average Cq values 15.01±0.86 to 19.32±0.10), which were absent in the non-transgenic counterpart. Detached leaf insect bioassay indicate larval mortality (up to 39.75%), reduced larval feeding (up to 82.91%) and reduced larval weight gain (up to 68.23%), compared to control lines. Evaluation of gene offers a platform to identify efficacious insecticidal gene that can be used for insect resistance management in chickpea.

Genetic modification of Gossypium arboreum universal stress protein (GUSP1) improves drought tolerance in transgenic cotton (Gossypium hirsutum)

Cotton crop suffers shortage of irrigation water at reproductive stage which reduces the yield and fibre quality. Universal stress proteins belong to Pfam00582 which enables several plants to cope with multiple stresses via ATP binding. GUSP1 (Gossypium arboreum USP) is one of such proteins; its amino acids were mutated after in silico simulations including homology modeling and molecular docking analysis. Transgenic cotton plants were developed through Agrobacterium mediated genetic transformation by using mutated pmGP1 and non mutated pGP1 constructs under CaMV35S promoter. PCR and semi-quantitative PCR analyses confirmed the amplification and expression of transgene in transgenic plants. It was revealed that leaf relative water content, total chlorophyll content, CO₂ assimilation as net photosynthesis, stomatal conductance, total soluble sugars and proline content was significantly increased at P ≤ 0.0001 and P ≤ 0.001 in both the pmGP1 and pGP1 transgenic plants as compared to non transgenic control plants. Moreover, relative membrane permeability and the transpiration rate were reduced significantly at P ≤ 0.0001 and P ≤ 0.001 respectively in transgenic plants under drought stress. Furthermore, the T1 transgenic seedlings containing pmGP1 mutated construct showed longer roots under desiccation stress imposed by 5% PEG. Transgene inheritance into the T1 progeny plants was confirmed by amplification through PCR and integration through Southern blot. Hence, our results pave the way to utilize the mutagenized known genes for increasing endurance of plants under drought stress. This will help to increase our understanding of drought tolerance/ sensitivity in cotton plants at the molecular level.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01048-5.

Prioritizing phthalate esters (PAEs) using experimental in vitro/vivo toxicity assays and computational in silico approaches

Phthalate esters (PAEs) pose prominent ecological risks owing to their multiplex toxicity potentials and ubiquitous detection in the environment. Therefore, this study aims to prioritize the individual and mixtures of six PAEs based on their toxicological implications using in vitro and vivo models exposed at environmentally relevant concentrations. Results were further confirmed using in silico Combination index (CI) and Independent action (IA), and molecular docking models. Among PAEs, DEHP revealed prominent in vitro/vivo toxicity followed by DEP, DBP, and DMP. Importantly, binary mixtures particularly C2-C6 and C11-C15 exhibited greater developmental toxicity, apoptosis, and perturbed the HPG pathway. The CI and IA models forecasted antagonistic and additive effects at Fa = 0.5 and Fa = 0.9 using in vitro Acinetobacter sp. Tox2. Conversely, in zebrafish, the IA model predicted mixture effects in the following order: additive > synergistic > antagonistic on the regulation of the HPG pathway, which was consistent with experimental results from Acridine Orange (AO) staining and apoptosis gene expression. Molecular docking for estrogen receptors (ERα, ERβ) revealed the highest binding energy scores for DEHP, compared to other PAEs. In short, our findings confirm that individual and mixtures of PAEs behave as xenoestrogens in the freshwater ecosystem with DEHP as a priority compound.

Current Insights on Vegetative Insecticidal Proteins (Vip) as Next Generation Pest Killers

Bacillus thuringiensis (Bt) is a Gram negative soil bacterium. This bacterium secretes various proteins during different growth phases with an insecticidal potential against many economically important crop pests. One of the important families of Bt proteins is vegetative insecticidal proteins (Vip), which are secreted into the growth medium during vegetative growth. There are three subfamilies of Vip proteins. Vip1 and Vip2 heterodimer toxins have an insecticidal activity against many Coleopteran and Hemipteran pests. Vip3, the most extensively studied family of Vip toxins, is effective against Lepidopteron. Vip proteins do not share homology in sequence and binding sites with Cry proteins, but share similarities at some points in their mechanism of action. Vip3 proteins are expressed as pyramids alongside Cry proteins in crops like maize and cotton, so as to control resistant pests and delay the evolution of resistance. Biotechnological- and in silico-based analyses are promising for the generation of mutant Vip proteins with an enhanced insecticidal activity and broader spectrum of target insects.

In silico design of two novel fusion proteins, p28-IL-24 and p28-M4, targeted to breast cancer cells

Background and purpose:

An anticancer peptide P28, has shown to be cytolethal on various cancer cells including breast cancer. Moreover, p28 can be also used as a targeting moiety in the structure of fusion proteins. IL-24 (or its truncated form, M4) is a cytokine with anticancer activity against a wide range of tumor cells. We aimed at production of a fusion protein consisted of p28 and either IL-24 or M4 to target breast cancer. However, selection of a proper linker to join the two moieties without intervening each other’s function is a key factor in the construction of fusion proteins. In the present study, the impact of different linkers on construction of the two chimeric proteins (p28-IL-24 and p28-M4) was assessed in silico.

Experimental approach:

After selection of some linkers with different lengths and characteristics, a small library of the chimeric proteins was created and assessed. Furthermore, following selection of the most suitable linker, the three-dimensional structures and dynamic behavior of both fusion proteins were evaluated by homology modeling and molecular dynamic simulation, respectively.

Findings / Results:

Based on the results, a rigid linker having the peptide sequences of AEAAAKEAAAKA showed highest freedom of action for both moieties.

Conclusion and implications:

Between the p28-IL-24 and p28-M4 fusion proteins, the former showed better stability as well as solubility and might show stronger anticancer effects in vitro and in vivo, because its peptide moieties showed to exert their activities freely.

Molecular Interaction-Based Exploration of the Broad Spectrum Efficacy of a Bacillus thuringiensis Insecticidal Chimeric Protein, Cry1AcF

Bacillus thuringiensis insecticidal proteins (Bt ICPs) are reliable and valuable options for pest management in crops. Protein engineering of Bt ICPs is a competitive alternative for resistance management in insects. The primary focus of the study was to reiterate the translational utility of a protein-engineered chimeric Cry toxin, Cry1AcF, for its broad spectrum insecticidal efficacy using molecular modeling and docking studies. In-depth bioinformatic analysis was undertaken for structure prediction of the Cry toxin as the ligand and aminopeptidase1 receptors (APN1) from Helicoverpa armigera (HaAPN1) and Spodoptera litura (SlAPN1) as receptors, followed by interaction studies using protein-protein docking tools. The study revealed feasible interactions between the toxin and the two receptors through H-bonding and hydrophobic interactions. Further, molecular dynamics simulations substantiated the stability of the interactions, proving the broad spectrum efficacy of Cry1AcF in controlling H. armigera and S. litura. These findings justify the utility of protein-engineered toxins in pest management.

A novel Vip3Aa16-Cry1Ac chimera toxin: Enhancement of toxicity against Ephestia kuehniella, structural study and molecular docking

Bacillus thuringiensis Vip3A protein has been widely used for crop protection and for delay resistance to existing insecticidal Cry toxins. During current study, a fusion between vip3Aa16 and the toxic core sequence of cry1Ac was constructed in pHT Blue plasmid. Vip3Aa16-Cry1Ac protein was expressed in the supernatant of B. thuringiensis with a size of about 150 kDa. Bioassays tested on Ephestia kuehniella showed that the use of the chimera toxin as biopesticide improved the toxicity to reach 90% ± 2 with an enhancement of 20% compared to the single Vip3Aa16 protein. The findings indicated that the fusion protein design opens new ways to enhance Vip3A toxicity against lepidopteran species and could avoiding insect tolerance of B. thuringiensis delta-endotoxins. Through computational study, we have predicted for the first time the whole 3D structure of a Vip3A toxin. We showed that Vip3Aa16 structure is composed by three domains like Cry toxins: an N-terminal domain containing hemolysin like fold as well as two others Carbohydrate Binding Module (CBM)-like domains. Molecular docking analysis of the chimera toxin and the single Vip3Aa16 protein against specific insect receptors revealed that residues of CBM like domains are clearly involved in the binding of the toxin to receptors.